No clean solder paste now most companies are still using the traditional electronic assembly, however, more advanced products is emerging. Provide better the solder paste printing performance, wide reflow curve range and stronger probe can test, but also provide stable and consistent product shelf life and batch consistency. This paper summarizes the new progress of cleaning free solder paste.
1, characteristics
Traditional solder paste only in printing is meet the requirements, they were never idle time (printers, downtime), printing speed and shear thinning aspects for by the end of the school to provide a wide range of process, this will cause the defects, the speed of production lines from scrap restrictions and solder paste. The new product has a wide range of technology in these three aspects.
According to the estimation of defect SMT defect 50% is caused by the printing process template. These defects are mainly due to the amount of each of the solder paste printing is inconsistent. In order to reduce the defects related to printing, printing process is to ensure that every time in each pad printing uniform quantity. Therefore, changes in the stability of solder paste printing conditions will become the key to reduce the defect rate. The new paste can achieve consistent printing quantity, any idle time, printing speed and shear thinning.
2, idle time
Idle time is set for the most long time template printing machine for maintenance or other reasons and allowed to stop, in the idle time after the first printing without any printing defects. The idle time for the traditional 10-20min solder paste, solder paste new can not dry or idle 60-120min printing problems.
After each printing stroke will have a small amount of solder paste in hole in the template. This will paste in the opening, drying and preventing the idle time after the first printing paste clean cavity from template. If the idle time of 60min, the old solder paste products will require 5-10 printing after the trip in order to achieve effective printing. New products in the long downtime for the first time after printing can achieve acceptable printing, it reduces waste and improves the speed of the production line.
This improvement is to adjust the use of solvent system results in the chemical composition of solder paste. A solvent with low evaporation rate at room temperature, thus reducing the dry phenomenon. This greatly increases the scope of technology of screen printing machine, allowing the operator in maintenance, shifts, production line or change the operating a moment's rest stop after the resumption of production.
3, the printing speed
From the early 1990s to the mid, maximum printing speed of most of the solder paste is designed to 2.54-5.08cm/s, because of a SMT Engineer that the entire production line speed depends not only on the stencil printing machine speed. Therefore, the printing speed is set very low, rolling performance and printing to the best solder paste. However, with the rapid development of SMT equipment, SMT production line speed is greatly improved, the template printers often become a bottleneck in the production process. This leads to SMT Engineer Requirements for soldering paste can be achieved 10.16-20.32cm/s printing speed, and in the printing quality without any substantial degradation.
If you use the traditional solder paste in the application of high speed printing. The result will be lack of adverse rolling and fine gap region of the coating amount. The new product has reduced the viscosity and viscosity, it can make the paste into the fine clearance holes, thereby improving the printing speed. Paste the most advanced to 2.54 or 20.32cm/s the speed of coating paste volume right.
Reduced viscosity is helpful to improve the traditional solder paste printing speed and idle time, but only simply decreases the viscosity will not be able to solve these problems. Decrease the viscosity of some other problems, including cooling slump, bad block definition (potential bridging) and adverse temperature and humidity stability. Therefore reduced without increasing the viscosity of solder paste slump is very important. The solder paste can improve the printing speed and idle time without causing more related defects and slump. The viscosity and slump are not necessarily related, reduce the viscosity of the solder paste is easy to slump, but this is not the inevitable result. Slump solder paste can be improved through the chemical composition of the solder paste adjustment performance, solder paste viscosity decreased in slump performance without any change.
The combination of high speed printing, high speed printing and increasing roller pressure can be caused by the combination of high speed printing and high speed printing process.
4, shear thinning
Shear thinning is refers to the solder paste under pressure the viscosity is destroyed, the larger pressure will cause greater viscosity lost, which will contribute to bridging defects. Therefore solder paste maker facing the challenge is to develop a product, the product can withstand high pressure (after high speed and roller printing pressure) without loss of performance of viscosity. Traditional solder paste under the environment of high-speed printing its viscosity is damaged very fast, and pastes can improve printing speed and without marked thinning. Thinning directly affect the viscosity and printing of solder paste, solder paste is made to minimize the thinning target.
If solder paste during the printing operation is relatively stable and with the printing speed and idle time has nothing to do can achieve consistent print quality. The most advanced solder paste to long-term stable printing, and the printing speed, pressure roller, idle time or solder paste using time independent.
5, reflow soldering
Each kind of solder paste have technical board, the report describes the best solder paste or recommended curve. However, many SMT processes cannot follow these curves. With the board style (size, thickness and density)